Plastic lenses are lightweight, highly tough and easy to be dyed. Properties particularly required for plastic lenses are: low specific gravity; high transparency; low yellowness; high refractive index and high Abbe number as optical properties; high heat resistance; high strength; and the like. A high refractive index allows a lens to be thinner, and a high Abbe number reduces the chromatic aberration of a lens.
Recently, many examples using an organic compound having a sulfur atom for providing a high refractive index and a high Abbe number have been reported. Among such examples, polyepisulfide compounds having a sulfur atom are known to provide a good balance between the refractive index and the Abbe number (Patent Document 1). Further, since polyepisulfide compounds can be reacted with various compounds, for the purpose of the improvement of physical properties, compositions in combination with various compounds have been proposed (Patent Documents 2-5).
However, it is difficult to store an episulfide compound for a long period of time because of its high reactivity. In this regard, techniques of keeping in cold storage (Patent Document 6) and techniques of adding an epoxy compound having a halogen group (Patent Document 7) have been proposed.